1. Field of the Invention
This invention relates to hydrocarbon conversion catalysts, such as those utilized to catalyze the reaction of hydrogen with organo-nitro, organo-metallic and particularly organo-sulfur compounds. More particularly this invention is directed to a catalyst useful for the hydrodesulfurization of hydrocarbons, such as gas oils and residuum, and to a method for preparing such catalysts by employing a novel aqueous impregnating solution. The invention is especially directed to catalysts of high overall desulfurization activity and stability.
2. Description of the Prior Art
In the refining of hydrocarbons, it is often necessary to convert a hydrocarbon fraction to different forms. Typically, particulate catalysts are utilized to promote desulfurization, denitrogenation or demetallization reactions when feedstocks such as gas oils or residuum are contacted with catalysts under conditions of elevated temperature and pressure and in the presence of hydrogen so that the sulfur components are converted to hydrogen sulfide, the nitrogen components to ammonia and the metals are deposited on the catalyst.
Conversions of hydrocarbons are often carried out with a catalyst containing Group VIB and Group VIII metals and phosphorous on a refractory oxide support. Compositions containing these and other elements have been previously investigated. For example, catalysts comprising a Group VIB metal, particularly molybdenum or tungsten, a Group VIII metal, particularly cobalt or nickel, and phosphorous on an alumina base have been disclosed in U.S. Pat. Nos. 3,755,196 and 3,840,472. Such catalysts are very often prepared by impregnation, that is, the deposition of the active components on the support base by contact thereof with an aqueous solution containing the active components in dissolved form. U.S. Pat. No. 3,755,196, for example, describes impregnating media and methods for preparing catalysts using stabilized impregnating solutions consisting of molybdenum plus nickel or cobalt salts with phosphoric acid dissolved in an aqueous medium. U.S. Pat. No. 3,840,472 discloses another process for preparing a stable impregnating solution that includes dissolving a nickel or cobalt compound with an acid of phosphorous followed by subsequent dissolution of molybdenum oxide. The presence of phosphorus in many conventional catalysts is apparently due to the method of catalyst preparation rather than just for catalytic activity and stability.
Although conventional catalysts, including those requiring phosphorous in their preparation, are active and stable for hydrocarbon conversion reactions, catalysts of yet higher activities and stabilities are still being sought, irrespective of phosphorous requirements. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of a catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur, nitrogen, and/or contaminant metals content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended due to such factors as lower coke formation or the deposition of less metals.
It is generally accepted that greater active component uniformity in the catalytic particles improves activity. The formation of a more evenly distributed layer of the active components, such as the metals and their oxides, or sulfides, in sufficient concentration throughout the surface area of the catalytic support provides more efficient utilization of the catalytic contacting surface.
Accordingly, it is an object of this invention to provide hydrocarbon conversion catalysts having a relatively evenly distributed layer of active components and to provide a method for using such catalysts for the desulfurization, denitrogenation, and/or demetallization of hydrocarbons. Another object is to provide hydrocarbon conversion catalysts of improved desulfurization activity and stability in comparison to conventional catalysts. Yet another object is to provide a catalyst of improved demetallization and denitrogenation activity.
It is a further object of the invention to provide a method for preparing a hydrocarbon conversion catalyst. It is a further object still to provide a method for preparing hydrocarbon conversion catalysts of improved desulfurization activity and stability in comparison to conventional catalysts. Another object is to provide a method for preparing a catalyst of improved demetallization and/or denitrogenation activity. Yet another object is to provide an impregnating solution having long term stability that may be utilized for preparing hydrocarbon conversion catalysts. These and other objects and advantages of the invention will be apparent from the following description.